Compositions of <i>n</i>-alkanes and <i>n</i>-alkanoic acids released by thermochemolysis with tetramethylammonium and trimethylsulfonium hydroxides of a type II kerogen

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  • Ogata Shuji
    Department of Natural History Sciences, Faculty of Science, Hokkaido University
  • Miyata Yuma
    Department of Natural History Sciences, Faculty of Science, Hokkaido University
  • Sawada Ken
    Department of Natural History Sciences, Faculty of Science, Hokkaido University

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  • Compositions of n-alkanes and n-alkanoic acids released by thermochemolysis with tetramethylammonium and trimethylsulfonium hydroxides of a type ⅠⅠ kerogen

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Abstract

The type II kerogen from the Miocene Onnagawa Formation Shale was analyzed by pyrolysis and thermochemolysis with tetramethylammonium hydroxide (TMAH) and trimethylsulfonium hydroxide (TMSH) under various thermal conditions. The results were compared with that by alkali hydrolysis. The n-alkanes and n-alkenes in products by pyrolysis and thermochemolysis might be generated from alkyl moieties in geomacromolecule by thermal cracking of C-C bonds. The n-alkanoic acids (as fatty acid methyl esters; FAMEs) were mainly detected in the compounds released from the kerogen by thermochemolysis, indicating that they have been preserved through polymerization of marine plankton-derived compounds. Noticeably, the short chain (<C11) FAMEs were abundant in products by thermochemolysis, while those were hardly detected in hydrolysates. These short chain n-alkanoic acids might be mainly occluded in intra-aggregates within the geomacromolecule. In addition, the C7 and C9 FAMEs predominated in products by TMSH-using thermochemolysis, although the C7 FAME was minor in TMAH method. It was suggested that the trapped and occluded compounds like C7 and C9 acids were more efficiently released from kerogen by TMSH thermochemolysis. On the other hand, total FAME/n-alkane ratios in the products by TMAH thermochemolysis were significantly higher than those by TMSH method. These results suggest that total recovery of the FAME released from kerogen by thermochemolysis can be lower in the presences of TMSH than TMAH.

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